HashSet in java

In this previous post, we have seen how to Iterate over a Vector. In this post, we will learn about HashSet in java.

HashSet has the following features.

  • HashSet implements Set interface.
  • It does not maintain any insertion order. Elements would be returned in any random order.
  • Allows only unique value. If we try to add duplicate elements, then old value will be overwritten.
  • HashSet is non-synchronized.
  • HashSet allows null values however if you insert more than one nulls it would still return only one null value.


HashSet<ObjectType> name = new HashSet<ObjectType>();


import java.util.HashSet;

public class HashSetExample {

	public static void main(String[] args) {
		HashSet<String> cars = new HashSet<String>();
		//Add duplicate elements
		//Addition of null values
		//Display the hashset
		System.out.println("HashSet : "+cars);



HashSet : [null, Bugatti, BMW, Ferrari, Honda, Mercedes]


HashSet Methods:

  • boolean add(Element  e): It adds the element e to the HashSet.
  • void clear(): It removes all the elements from the Set.
  • Object clone(): This method returns a shallow copy of the HashSet.
  • boolean contains(Object o): It checks whether the specified Object o is present in the list or not. If the object has been found it returns true else false.
  • boolean isEmpty(): Returns true if there is no element present in the Set.
  • int size(): It gives the number of elements of a Set.
  • boolean remove(Object o): It removes the specified Object o from the Set.
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Shekhar Sharma

Shekhar Sharma is founder of testingpool.com. This website is his window to the world. He believes that ,"Knowledge increases by sharing but not by saving".